The present invention relates to shell-side feed, gas separation devices or modules which use hollow fiber membranes that exhibit selective permeability to fluids such as gases. The invention may also be used in vaporization or liquid separation devices or modules.
Prior art shell-side feed, hollow fiber, gas separation modules have each end of the hollow fibers encased or encapsulated in a tubesheet, with one tubesheet located toward a feed gas inlet side of the device and the other tubesheet located toward a permeate gas flow outlet. If a counter-current flow arrangement is desired—i.e., between the gas flowing on the permeate side of the hollow fibers and that flowing on the non-permeate side—then one tubesheet has the permeate gas flow to it blocked, thereby blocking the hollow fiber bores on the non-permeate fluid outlet end. This blocked tubesheet then becomes an obstruction to the feed gas flow.
Usually the fiber bore blocking is done by encasing the entire end of the fiber bundle in a tubesheet where the fibers do not extend all the way through. If the fiber ends were open while this non-permeate side tubesheet is formed, then the fibers will be plugged with the tubesheet potting material as well as being collectively encased.
The hollow fiber bores are only required to be open on the non-permeate fluid outlet end if a sweep gas will be introduced. If the tubesheet is finished to have both ends of the fibers opened then the tubesheet located toward the non-permeate fluid outlet end will have to be blocked by another means such as a plate or painting the tubesheet face with a material that plugs the fibers.
Some designs attempt to mitigate the obstruction problem by using tubes to create discrete flow paths through the blocked tubesheet (see e.g., U.S. Pat. No. 5,207,906 to Auvil et al.). Other designs include fiber loops which begin and end in the same tubesheet, thereby eliminating the blocked tubesheet.
A need exists for a shell-side feed, hollow fiber, fluid separation module that can efficiently handle a counter-current flow arrangement without obstructing feed fluid flow while preventing feed fluid from leaking into the bore of the hollow fiber membranes.